react-hooks-testing-library

Simple component wrapper and utilities for testing React hooks.

The problem

You're writing an awesome custom hook and you want to test it, but as soon as you call it you see the following error:

Invariant Violation: Hooks can only be called inside the body of a function component.

You don't really want to write a component solely for testing this hook and have to work out how you were going to trigger all the various ways the hook can be updated, especially given the complexities of how you've wired the whole thing together.

The solution

The react-hooks-testing-library allows you to create a simple test harness for React hooks that handles running them within the body of a function component, as well as providing various useful utility functions for updating the inputs and retrieving the outputs of your amazing custom hook.

Similarly to react-testing-library, which this library draws much of it's inspiration from, it aims to provide a testing experience as close as possible to natively using your hook from within a real component.

Using this library, you do not have to concern yourself with how to construct, render or interact with the react component in order to test your hook. You can just use the hook directly and assert the results.

When to use this library

You're writing a library with one or more custom hooks that are not directly tied a component
You have a complex hook that is difficult to test through component interactions

When not to use this library

Your hook is defined along side a component and is only used there
Your hook is easy to test by just testing the components using it

Example

// useCounter.js
import { useState, useCallback } from 'react'

function useCounter() {
  const [count, setCount] = useState(0)

  const increment = useCallback(() => setCount((x) => x + 1), [])
  const decrement = useCallback(() => setCount((x) => x - 1), [])

  return { count, increment, decrement }
}

export default useCounter

// useCounter.test.js
import { renderHook, act } from 'react-hooks-testing-library'
import useCounter from './useCounter'

test('should increment counter', () => {
  const { result } = renderHook(() => useCounter())

  act(() => result.current.increment())

  expect(result.current.count).toBe(1)
})

test('should decrement counter', () => {
  const { result } = renderHook(() => useCounter())

  act(() => result.current.decrement())

  expect(result.current.count).toBe(-1)
})

Installation

npm install --save-dev react-hooks-testing-library

API

`renderHook(callback[, options])`

Renders a test component that will call the provided callback, including any hooks it calls, every time it renders.

Note: testHook has been renamed to renderHook. testHook will continue work in the current version with a deprecation warning, but will be removed in a future version.

You should update any usages of testHook to use renderHook instead.

Arguments

callback (function()) - function to call each render. This function should call one or more hooks for testing.
options (object) - accept the following settings:
- initialProps (object) - the initial values to pass to the callback function
- wrapper (component) - pass a React Component as the wrapper option to have it rendered around the inner element. This is most useful for creating reusable custom render functions for common data providers

Returns

result (object)
- current (any) - the return value of the callback function
- error (Error) - the error that was thrown if the callback function threw an error during rendering
waitForNextUpdate (function) - returns a Promise that resolves the next time the hook renders, commonly when state is updated as the result of a asynchronous action.
rerender (function([newProps])) - function to rerender the test component including any hooks called in the callback function. If newProps are passed, the will replace the initialProps passed the the callback function for future renders.
unmount (function()) - function to unmount the test component, commonly used to trigger cleanup effects for useEffect hooks.

`act(callback)`

This is the same act function that is exported by react-test-renderer.

Contributors

Thanks goes to these wonderful people (emoji key):

_{Michael Peyper} 💻 🎨 📖 🤔 🚇 📦 ⚠️ 🔧	_otofu-square 💻	_{Patrick P. Henley} 🤔 👀	_{Matheus Marques} 💻	_{Dhruv Patel} 🐛 👀	_{Nathaniel Tucker} 🐛 👀	_{Sergei Grishchenko} 💻 📖 🤔
_{Josep M Sobrepere} 📖